1. Technical Field
The present invention relates to switched-mode electronic power devices, in which integrated circuits are used for driving high-voltage switches and in which a start-up circuit is also required to be used.
2. Description of the Related Art
Among the electronic power devices for switched-mode applications, there are also Switched Mode Power Supplies (SMPS).
To the purpose, the U.S. Pat. No. 5,313,381 describes, with reference to the prior art, an SMPS power supply comprising a rectifier and an input filter connected to a primary of a transformer. The secondary of this transformer is connected to a rectifier and an output filter being provided with terminals in order to supply a load with a direct voltage.
The primary of the transformer is connected to a MOSFET (Metal Oxide Semiconductor Field Effect Transistor) switch that is intended to be driven by a PWM (Pulse Width Modulation) controller.
In an initial step, i.e., during the step of starting up the power supply, the PWM is caused to operate by a start-up network, which can be deactivated after the start-up has been carried out, based on the particular type of application.
A suitable performance/cost ratio is particularly difficult to achieve when manufacturing these switched-mode devices. This is mainly due to the fact that these devices have high-voltage components, such as the switching MOSFET and several components of the start-up network, and components that can be low-voltage (typically the PWM controller).
The self-contained integration of high-voltage components with low-voltage ones has some problems, which are not easily conciliated with the requirement of reducing the manufacturing cost by minimizing the number of electronic components external to the chip. The solutions to this problem that have been provided so far prove to be unsatisfactory.